The present invention generally relates to semiconductor devices, methods of producing semiconductor devices and semiconductor device mounting structures, and more particularly to a semiconductor device which has only a portion of leads exposed at a bottom surface of a package so as to improve the packaging density of the semiconductor device, a method of producing such a semiconductor device, and a semiconductor device mounting structure for mounting such a semiconductor device.
Due to the recent improvements in reducing the size, increasing the operation speed and increasing the functions of electronic equipments, there are demands to realize similar improvements in semiconductor devices. In addition to these demands on the semiconductor devices per se, there are also demands to improve the packaging density of the semiconductor device when packaging the semiconductor device on a substrate.
Accordingly, although the majority of the existing semiconductor devices employ the surface mounting which connects the leads at the surface of the substrate, there are demands to further improve the packaging density of the semiconductor devices.
FIG. 1 shows a perspective view of an example of a conventional semiconductor device 1. FIG. 2 is a cross sectional view of this semiconductor device 1 taken along a line Axe2x80x94A in FIG. 1. For example, this type of semiconductor device was proposed in Japanese Laid-Open Patent Applications No. 63-15453 and No. 63-15451.
In FIGS. 1 and 2, the semiconductor device 1 generally includes a semiconductor chip 2, a resin package 3 which encapsulates the semiconductor chip 2, a plurality of leads 4, and a stage 7 on which the semiconductor chip 2 is mounted. One end 4a of the lead 4 is connected to the semiconductor chip 2 via a wire 5, and the other end of the lead 4 is exposed at a bottom surface 3a of the package 3 to form an external terminal 6. In other words, all parts of the semiconductor device 1 excluding the external terminals 6 of the leads 4 are encapsulated within the package 3.
Because the external terminals 6 of the leads 4 are exposed at the bottom surface 3a of the package 3 in this semiconductor device 1, the projecting length of the leads 4 on the outer side of the package 3 can be made small, thereby making it possible to improve the packaging density. In addition, the external terminals 6 of the leads 4 do not need to be bent as in the case of the conventional leads having the L-shape or gull-wing shape. As a result, no mold is required to bend the external terminals 6, thereby making it possible to simplify the production process and to reduce the production cost.
On the other hand, another type of semiconductor device was proposed in a Japanese Laid-Open Patent Application No. 4-44347. According to this proposed semiconductor device, the leads are fixed to a circuit forming surface of the semiconductor chip via an insulative adhesive agent. In addition, the size of the package is reduced by encapsulating only the circuit forming surface or only the circuit forming surface and side surfaces of the semiconductor chip.
However, according to the semiconductor device 1 described above, the end 4a of the lead 4 is located on both sides of the semiconductor chip 2. As a result, there is a limit to reducing the size of the package 3, and there was a problem in that the size of the semiconductor device 1 cannot be reduced to a sufficient extent. In other words, the size of the semiconductor device ideally is approximately the same as the size of the semiconductor chip. However, the size of the semiconductor device 1 is approximately two or more times greater than the size of the semiconductor chip 2.
In addition, the semiconductor device 1 does not take the heat radiation into any consideration. That is, there was a problem in that the semiconductor device 1 cannot efficiently radiate the heat generated from the semiconductor chip 2 outside the package 3.
On the other hand, according to the semiconductor device proposed in the Japanese Laid-Open Patent Application No. 4-44347, the leads which are connected to an external substrate are apart from the package, and thus, the transfer mold technique cannot be employed as the package forming technique, and the troublesome potting technique must be employed. As a result, this proposed semiconductor device requires troublesome processes to produce, and there were problems in that the production efficiency of the semiconductor device is poor and the production cost of the semiconductor device is high. It is theoretically possible to produce this semiconductor device by employing the transfer mold technique, however, this would require the mold to be made up of a large number of split molds, and this technique is impractical in that the mold would become extremely expensive.
Accordingly, it is a general object of the present invention to provide a novel and useful semiconductor device and a method of producing the same, in which the problems described above are eliminated.
A first particular object of the present invention is to provide a semiconductor device and a method of producing the same, which can sufficiently reduce the size of the semiconductor device.
Another and more specific object of the present invention is to provide a semiconductor device comprising a semiconductor chip having a top surface and a bottom surface, a plurality of leads arranged under the bottom surface of the semiconductor chip, where the leads have first ends electrically coupled to the semiconductor chip and second ends which form external terminals and each of the external terminals have a bottom surface, and a package encapsulating the semiconductor chip and the leads so that the bottom surface of each of the external terminals is exposed at a bottom surface of the package and remaining portions of the leads are embedded within the package, where the package has a size which is approximately the same as that of the semiconductor chip in a plan view viewed from above the top surface of the semiconductor chip. According to the semiconductor device of the present invention, it is possible to considerably reduce the size of the semiconductor device to approximately the same size as the semiconductor chip in the plan view.
Still another object of the present invention is to provide a method of producing a semiconductor device comprising the steps of (a) press-working a lead frame and forming a plurality of leads which extend inwards to a predetermined position where a semiconductor chip is to be mounted, (b) mounting the semiconductor chip at the predetermined position on a stage, where the steps (a) and (b) are carried out in an arbitrary order, (c) wire-bonding first ends of the leads to the semiconductor chip via wires, and (d) encapsulating the semiconductor chip and the leads by a resin package so that a bottom surface of the leads is exposed at second end at a bottom surface of the resin package. According to the method of producing the semiconductor device of the present invention, it is possible to produce the semiconductor device which is considerably small compared to the conventional semiconductor device using simple processes. In addition, since the leads are embedded within the resin package and the second ends (external terminals) of the leads are exposed at the bottom surface of the resin package, it is possible to employ the transfer mold technique as the package forming technique. As a result, it is possible to form the resin package with ease and improve the production yield and also reduce the production cost.
A second particular object of the present invention is to provide a semiconductor device and a semiconductor device mounting structure, which can relieve a stress which is generated due to a difference between coefficients of linear thermal expansion of the semiconductor device and a circuit substrate, so as to improve the mounting characteristic and reliability of the semiconductor device when mounting the semiconductor device on the circuit substrate.
A further object of the present invention is to provide a semiconductor device comprising a semiconductor chip, a package encapsulating the semiconductor chip, the package having a wall surface, a plurality of leads each having one end electrically connected to the semiconductor chip and another end exposed at the wall surface of the package to form an external terminal, each of the leads excluding the external terminal being encapsulated within the package, and a lead projection provided on the external terminal of the lead, the lead projection projecting from the wall surface of the package. According to the semiconductor device of the present invention, it is possible to increase a thickness of a soft bonding material which is arranged on the external terminal when mounting the semiconductor device on a circuit substrate, as compared to the conventional semiconductor device having no lead projection, and a stress when generated can be satisfactorily absorbed by the soft bonding material having the increased thickness, thereby preventing a crack from being formed in the package.
Another object of the present invention is to provide a semiconductor device comprising a semiconductor chip, a package encapsulating the semiconductor chip, the package having a wall surface, a plurality of leads each having one end electrically connected to the semiconductor chip and another end exposed at the wall surface of the package to form an external terminal, each of the leads excluding the external terminal being encapsulated within the package, and a package projection provided on the wall surface of the package where the external terminal of the lead is exposed, the package projection projecting with respect to the external terminal. According to the semiconductor device of the present invention, it is possible to increase a thickness of a soft bonding material which is arranged on the external terminal hen mounting the semiconductor device on a circuit substrate, as compared to the conventional semiconductor device having no lead projection, and a stress when generated can be satisfactorily absorbed by the soft bonding material having the increased thickness, thereby preventing a crack from being formed in the package.
Still another object of the present invention is to provide a semiconductor device comprising a semiconductor chip, a package encapsulating the semiconductor chip, the package having a wall surface, a plurality of leads each having one end electrically connected to the semiconductor chip and another end exposed at the wall surface of the package to form an external terminal, each of the leads excluding the external terminal being encapsulated within the package, and a lead recess provided on the external terminal of the lead, the lead recess being caved in from the wall surface of the package. According to the semiconductor device of the present invention, it is possible to increase a thickness of a soft bonding material which is arranged on the external terminal when mounting the semiconductor device on a circuit substrate, as compared to the conventional semiconductor device having no lead recess, and a stress when generated can be satisfactorily absorbed by the soft bonding material having the increased thickness, thereby preventing a crack from being formed in the package.
A further object of the present invention is to provide a semiconductor device mounting structure for mounting a semiconductor device on a surface of a circuit substrate using a soft bonding material, the semiconductor device comprising a semiconductor chip, a package encapsulating the semiconductor chip and having a wall surface, and a plurality of leads each having one end electrically connected to the semiconductor chip and another end exposed at the wall surface of the package to form an external terminal, each of the leads excluding the external terminal being encapsulated within the package, where the semiconductor device mounting structure comprises a spacer supporting the semiconductor device on the circuit substrate in a state where the semiconductor device is separated from the surface of the circuit substrate, a gap being formed between the semiconductor device and the circuit substrate, and a soft bonding material arranged at the gap and bonding the semiconductor device and the circuit substrate. According to the semiconductor device mounting structure of the present invention, it is possible to increase a thickness of a soft bonding material which is arranged on the external terminal when mounting the semiconductor device on the circuit substrate, as compared to the conventional semiconductor device mounting structure having no spacer, and a stress when generated can be satisfactorily absorbed by the soft bonding material having the increased thickness, thereby preventing a crack from being formed in the package. As a result, the mounting characteristic and reliability of the semiconductor device is improved when mounting the semiconductor device on the circuit substrate.
Another object of the present invention is to provide a semiconductor device mounting structure for mounting a semiconductor device on a surface of a circuit substrate using a soft bonding material, the semiconductor device comprising a semiconductor chip, a package encapsulating the semiconductor chip and having a wall surface, and a plurality of leads each having one end electrically connected to the semiconductor chip and another end exposed at the wall surface of the package to form an external terminal, each of the leads excluding the external terminal being encapsulated within the package, the soft bonding material being arranged on the external terminal of on connecting electrodes provided on the circuit substrate, where the semiconductor device mounting structure comprises a bonding portion bonding the external terminal of the semiconductor device to the connecting electrode of the circuit substrate at a first location of the semiconductor device, and a bonding portion bonding the external terminal of the semiconductor device to the connecting electrode of the circuit substrate at a second location of the semiconductor device different from the first location, where a distance between the semiconductor device and the circuit substrate at the first location is greater than that at the second location, and an amount of soft bonding material forming the first bonding portion is greater than an amount of soft bonding material forming the second bonding portion. According to the semiconductor device mounting structure of the present invention, it is possible to positively bond and connect the semiconductor device and the circuit substrate even if a warp is generated in the semiconductor device.
Still another object of the present invention is to provide a semiconductor device comprising a semiconductor chip, a package encapsulating the semiconductor chip, the package having a wall surface, a plurality of leads each having one end electrically connected to the semiconductor chip and another end exposed at the wall surface of the package to form an external terminal, each of the leads excluding the external terminal being encapsulated within the package, and a lead projection provided on the external terminal of the lead, the lead projection projecting from the wall surface of the package and having a width which is smaller at a tip end portion of the lead projection than at the wall surface of the package. According to the semiconductor device of the present invention, it is possible to increase an area of the external terminal that is plated, thereby improving the wetting characteristic with respect to solder and also improving the reliability when bonding the semiconductor device and the circuit substrate.
A further object of the present invention is to provide a semiconductor device comprising a semiconductor chip, a package encapsulating the semiconductor chip, the package having a wall surface, a plurality of leads each having one end electrically connected to the semiconductor chip and another end exposed at the wall surface of the package to form an external terminal, each of the leads excluding the external terminal being encapsulated within the package, and a lead projection provided on the external terminal of the lead, the lead projection projecting from the wall surface of the package and having a thickness which is smaller at a tip end portion of the lead projection than at the wall surface of the package. According to the semiconductor device of the present invention, it is possible to increase an area of the external terminal that is plated, thereby improving the wetting characteristic with respect to solder and also improving the reliability when bonding the semiconductor device and the circuit substrate.
Another object of the present invention is to provide a method of producing a semiconductor device comprising a device body producing step, electrically coupling leads and a semiconductor chip, and producing a device body by encapsulating the semiconductor chip by a resin package so that portions of the leads are exposed from the resin package, a honing step, carrying out a honing process using a polishing solution at least with respect to a resin flash adhered on the portions of the leads exposed from the resin package, an etching step, removing an unwanted stacked layer structure formed on the leads by carrying out an etching process after the honing step, and a plating step, carrying out a plating process with respect to the leads after the etching step to form a plated layer made of a soft bonding material, where the honing step removes a portion of the unwanted stacked layer structure in addition to the resin flash. According to the method of producing the semiconductor device according to the present invention, a part of the unwanted stacked layer structure is also removed in addition to the resin flash by the honing step. Hence, the residual part of the unwanted stacked layer structure formed on the surface of the lead which is to be bonded to a circuit substrate is removed, thereby making it easier to remove the remaining unwanted stacked layer structure on the lead surface in the etching step which is carried out at a latter stage.
Still another object of the present invention is to provide a semiconductor device mounting structure for mounting a semiconductor device on a circuit substrate, where the semiconductor device has a plurality of leads each having one end electrically coupled to a semiconductor chip and another end exposed from a resin package to form an external terminal so that portions of each lead other than the external terminal are encapsulated within the resin package, the semiconductor device is mounted on the circuit substrate using a soft bonding material provided on external terminals or a plurality of connecting electrodes arranged on the circuit substrate, and the semiconductor device mounting structure comprises a recess formed in the resin package at a position in a vicinity where the leads are exposed from the resin package, and an under fill resin arranged between the semiconductor device and the circuit substrate, which under fill resin also filling the recess. According to the semiconductor device mounting structure of the present invention, the under fill resin is provided between the semiconductor device and the circuit substrate 218. By arranging the under fill resin between the semiconductor device and the circuit substrate, it is possible to absorb the stress generated due to the difference between the thermal expansions of the semiconductor device and the circuit substrate, even in the case of the semiconductor device having an external terminal formed by a portion of the lead exposed at the lower surface of the resin package, that is, even in the case of the semiconductor device having a construction such that the lead does not extend outwardly from the resin package. For this reason, it is possible to prevent the bonding part, that is, the mounted solder, between the lead and the circuit substrate from becoming damaged by a separation or the like, thereby improving the mounting reliability. On the other hand, the recess is formed at the position in the vicinity where the lead is exposed from the resin package. Hence, when mounting the semiconductor device on the circuit substrate, the under fill resin is also provided within the recess, and the bonding area between the under fill resin and the resin package increases, such that the under fill resin filled within the recess exhibits an anchor effect. Therefore, it is possible to improve the mounting reliability of the semiconductor device with respect to the circuit substrate, also from this point of view.
Other objects and further features of the resent invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.